The Role of Antipsychotic Plasma Levels in the Treatment of Schizophrenia

Antipsychotic drugs are highly efficacious in the treatment of positive psychotic symptoms of schizophrenia (1). However, a large fraction of patients either fail to respond to the prescribed antipsychotic drug or, while treatment responsive, are unable to tolerate the drug because of side effects. An approximation to the prevalence of these complicated courses of antipsychotic treatment may be gleaned from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) study (2), which found median rates of treatment discontinuation due to inefficacy and side effects of 25% and 15%, respectively. The challenge for prescribers is that the root cause of these complicated courses of antipsychotic treatment cannot be readily determined. Poor response may be caused by poor antipsychotic adherence, rapid elimination of the drug, or treatment resistance. Similarly, poor tolerance may be caused by slow elimination of the drug or high drug sensitivity. Because patient self-report and clinical intuition are unreliable sources of information to identify the cause of either presentation, treatment decisions are made under uncertainty.